Prepn by sulfonation of phenylhydrazine: L. Claisen, P. Roosen, Ann. 278, 296 (1894); by the reduction of p-diazobenzenesulfonic acid: Th. Zincke, A. Kuchenbecker, Ann. 330, 1 (1903); L. V. Lazeeva et al., SU 1057493 (1983 to Tambov Pigment), C.A. 100, 138755q (1984). Used in resoln of 2-pyrazoline cmpds: M. Mukai et al., Can. J. Chem. 57, 360 (1979); in isoln of volatile ketones: W. Treibs, H. Rhnert, Ber. 84, 433 (1951); in analysis of trace amounts of selenium: T. Kawashima et al., Anal. Chim. Acta 49, 443 (1970); eidem, ibid. 89, 65 (1977).